Sound reproducer



- 1927. May w. c. GRUNOW SOUND REPRODUCER Filed March 10. 1925 ,H/LL/ M (3, QP u/voW reamed May 31, 1927.

lTED STAT-es man "P rsr orrics.

WILLIAM C. GB'UNOW, 01' CHICAGO, ILLI'NbIS, ASSIGNOR ONE-HALF '10 BEBTRAM J. GBIGSBY, OF GZEIGAGO, ILLINOIS.

- SOUND BEPBODUGEB. I

Application illed'larch 10, was. Serial a... 14,527.

My invention relates to' telephones, particularly to loud speaking telephones, such as are frequently used in connection with wireless receiving apparatus.

5 In my experiments I have found that the elasticity or free vibratiliig movement of the diaphragm is sensibly a ected by a pumping action which the diaphragm, when vibrating, must perform inalternately compressing and sucking the air in the casing of the unit. This casing, for all practical purposes, is usually made air tight, and the conductors are le through a fairly tight outlet opening. A diaphragm, particularly in a loud speaking unit, should have perfect elasticity, that is, it should be able to respond efliciently through the entire range of variations in the voice currents without blasting or failing to reproduce clearly. The p 0 chief dificulty with the diaphragm, as heretofore constructed, is its inability to respond to weak currents as well as to strong currents, due to its lack of a free or natural vibrating movement. Unnecessary pressure 5 on the under side of the diaphragm due to condensation and rarefaction of'the air in the casing as the diaphragm vibrates has hindered to a certain extent this free or natural vibrating movement.

9 I An object of my invention is the provision of means for removing this impediment to the free action of the diaphragm, particularly by furnishing air holes or vents in the casing to relieve-any appreciable pressure or 5 suction effect on the diaphragm.

A further object of my invention resides in the adjustability of said air holes so as to vary, if desired, the pressure on the diaphragm. This variation may be made at 0 any time to secure improved results, if 1t 1s found that the action of the diaphragm Wlll be'assisted by a change in the pressure, either by relieving it entirely. or by allowmg it to be varied.

:5 My experiments have proved the value of this improvement. By closing the air holes while the unit is reproducing and by thereafter suddenly removing the closure from the openings, it will be easily noted that the volume of sound reproduced is perceptibly increased.

In order to apprise those skilled in the art how to construct and practice my invention, I shall now describe an embodiment thereof ings forming a part hereof.

In the drawings:

Figure 1 is a vertical sectional view through a sound reproducing unit embodymg my invention;

Fig. 2 is a view of this unit with the cover removed, looking downwardly on the permanent magnet, the coils and the openings in the base of the casing, this view being drawn on a smaller scale than Fig. 1; 4

Fig. 3 is a view similar to Fig. 1, but illustrating merely the lower portion of the same to show the means I employ foropening and closing these openings in the base of the unit; and

Fig. 4 is a bottom plan view of the device shown in Fig. 3, but drawn on a smaller scale.

The sound reproducer 1 comprises a cap 2 and cup 3, in which a permanent magnet 4c and its coils 5 are carried, and a diaphragm 6 adapted to be seated in the cap 2.

Permanent magnet 4 is in'the form of-a horseshoe and is adapted to have its ends secured to the base 7 of cup 3 by means of bolts 8. Pole pieces 10 extend inwardly from the ends of permanent magnet 4, having their ends turned upwardly to receive the coils 5. Coils 5 may be of any standard construction, comprising the ordinary spools about which winding 11 may be suitabl wound. The winding of each spool is pref n connection with the accompanying drawerably attached to terminals 12, secured by bolts 13 upon a strip of insulation 14. Terminals 12 are formed with opposed terminal lugs 15, spaced apart a predetermined distance to permit the current to jump the air gap in the event of an overload in the telephone circuit, thereby preventing the overload from burning out the windin s 11. As seen in Fig. 4, the bolts 13 extend through the base 7 of on 3 for the purpose of permitting the con uctors of the te ephone circuit to be connected to the unit.

Openings 18 may. be furnished in base 7 of the cup 3. These openings may be of any suitable size and disposed in any desired manner. They are, however, of a size sulficient to relieve the pressure of condensation and rarefaction of the air within the chamber on the diaphragm when the latter vibrates. It will be noted that openings '18 are so disposed as to relieve the pressure equally on oppositesides of this chamber and by referring to Fig. 3, there will be seen a pair of shutters 19 furnished for the purpose of opening and closing these openings 18. Shutters 19 have an extension arm 20 pivotally mounted at :21 and connected to the intermediate links 22. The opposite ends of these intermediate linksare pivotally connected to an operating link 23.

Link 23 may be provided with a slot 24, in which a fixed pin 25 is guided, the purpose of which is to maintain the link in a suitable manner on the under side of the sound reproducing unit. A right angular projection 26 may be formed on link 23 and this right angular projection may extend to any distance, so as to be accessible for ma nipailation during the operation of the unit. Link 23 may be moved back and forth to swing the shutters 19 in either closed or open positions. The closed position is shown in full lines in Fig. 4, while the open position is shown in dotted lines.

Assume that the sound reproducing unit is in operation and it is desired to increase,

its volume. All that it is necessary for the operator to do is to grip the projection 26 and move it outwardly so as to swing the shutters 19 away from the openings 18. The mechanical connection to the shutters may be arranged to move the shutters only partially from over the openings 18, so as to vary the sound by relieving only a part of the pressure in the chamber.

I have found that the above construction has given good results and not only has increased the volume, but has produced better 'tone qualit Many ot er forms in which this invention may be embodied will occur to those skilled in the art and the fact that I have specifical ly illustrated and described but one of then is notintended as a limitation.

I claim:

1. Sound reproducing means comprising i1 combination a casing, a diaphragm, electrica means for vibrating said diaphragm, ant means for varying the air pressure agains said diaphragm, said means including open ings in said casing and pivotally mountet shutter members serving as adjustableclc sures for said openings, links extending fro) the ends of said shutter members, and a: operating element pivotall) connected t said links for common control of said shut ters at a remote point from said openings 2. Means for controlling a plurality 0 shutters for openings provided in a casing c an electrically operated telephone unit t vary the pressure against one side of the dia phragm thereof comprising toggle mecha nism operativcly connected to said shutter:

and a common operating element opcrativel connected to said links to provide a rcmot control for said shutters.

3. Means for preventing the action of th air within the diaphragm chamber from hi1: dering the free vibratory movement of diaphragm of an electrically operated teh; phone unit comprising a plurality of shut ters serving as closures for openings com municating with said chamber, and a rt: motely operated lever operatively connecte to said shutters and extending outwardly a a distance to provide a common control l'o said shutters.

In witness whereof I have hereunto sub scribed my name.

WILLIAM G. GRUN OW. 

